Organometallics 2008, 27, 4005–4008
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Notes The Phosphaalkene-like Reactivity of Dithienophosphinines Ngoc Hoa Tran Huy,* Bruno Donnadieu, and Franc¸ois Mathey* UCR-CNRS Joint Research Chemistry Laboratory, Department of Chemistry, UniVersity of California, RiVerside, California 92521-0403 ReceiVed April 10, 2008 Summary: 2-Thienyldithienophosphinine (3) has been prepared in three steps starting by the ring expansion of dithienophosphole (4) upon reaction with 2-thiophenecarboxylic acid chloride, triethylamine, and water. DFT calculations indicate that the replacement of the phenyl in 2-phenyldithienophosphinine (2) by the 2-thienyl substituent in 3 significantly reduces the HOMO-LUMO gap. Accordingly, 3 reacts cleanly and quantitatiVely with 2,3-dimethylbutadiene to giVe the [2+4] cycloadduct 11, whose structure has been confirmed by X-ray crystal structure analysis, whereas 2 reacts slowly and giVes the adduct in only 52% yield, and the analogous 2-phenylphosphaphenanthrene (1) giVes only an untractable mixture.
Introduction The work of Re´au on thienyl-substituted phospholes1 and Baumgartner on dithienophospholes2 has convincingly shown the value of phosphorus-modified oligothiophenes as building blocks for optoelectronic materials.3 On this basis, we have started an investigation of the synthesis and chemistry of the previously unknown dithienophosphinines.4 During our preliminary investigation, we have noticed two clues that suggest that the thieno annellation sharply modifies the properties of dithienophosphinines by comparison with their benzo analogues, i.e., the phosphaphenanthrenes.5 Whereas the final aromatization step leading to 1 takes place at 275 °C from the P-benzyl 1,2dihydro derivative, the significantly easier aromatization leading to 2 takes place at 250 °C from the P-phenyl 1,2-dihydro derivative. In addition, the 31P resonance of 2 (δ 31P 149 ppm) is strongly shifted to higher fields when compared to the * Corresponding author. E-mail:
[email protected]. (1) (a) Fischmeister, C.; Hissler, M.; Toupet, L.; Re´au, R. Angew. Chem., Int. Ed. 2000, 39, 1812. (b) Hay, C.; Fave, C.; Hissler, M.; Rault-Berthelot, J.; Re´au, R. Org. Lett. 2003, 5, 3467. (c) Fave, C.; Cho, T.-Y.; Hissler, M.; Chen, C.-W.; Luh, T.-Y.; Wu, C.-C.; Re´au, R. J. Am. Chem. Soc. 2003, 125, 9254. (d) Su, H.-C.; Fadhel, O.; Yang, C.-J.; Cho, T.-Y.; Fave, C.; Hissler, M.; Wu, C.-C.; Re´au, R. J. Am. Chem. Soc. 2006, 128, 983. (e) Sebastian, M.; Hissler, M.; Fave, C.; Rault-Berthelot, J.; Odin, C.; Re´au, R. Angew. Chem., Int. Ed. 2006, 45, 6152. (2) (a) Baumgartner, T.; Neumann, T.; Wirges, B. Angew. Chem., Int. Ed. 2004, 43, 6197. (b) Baumgartner, T.; Bergmans, W.; Ka´rpa´ti, T.; Neumann, T.; Nieger, M.; Nyula´szi, M. Chem.-Eur. J. 2005, 11, 4687. (c) Neumann, T.; Dienes, Y.; Baumgartner, T. Org. Lett. 2006, 8, 495. (d) Baumgartner, T.; Wilk, W. Org. Lett. 2006, 8, 503. (e) Dienes, Y.; Durben, S.; Ka´rpa´ti, T.; Neumann, T.; Englert, U.; Nyula´szi, L.; Baumgartner, T. Chem.-Eur. J. 2007, 13, 7487. (3) Reviews:(a) Baumgartner, T.; Re´au, R. Chem. ReV. 2006, 106, 4681. (b) Hobbs, M. G.; Baumgartner, T. Eur. J. Inorg. Chem. 2007, 3611. (4) Tran Huy, N. H.; Donnadieu, B.; Mathey, F. Organometallics 2007, 26, 6497. (5) Nief, F.; Charrier, C.; Mathey, F.; Simalty, M. Tetrahedron Lett. 1980, 21, 1441.
resonance of 1 (δ 31P 186 ppm), which lies in the normal zone for phosphinines.
These observations led us to prepare 2-thienyldithienophosphinine (3) and to compare the chemistry of 1, 2, and 3. This comparison demonstrates that the thiophene unit, both as substituent and annellating ring, significantly modifies the chemistry of phosphinines.
Results and Discussion 2-Thienyldithienophosphinine (3) was prepared as shown in eq 1. The phosphinine was isolated as yellow crystals (both 1 and 2 are colorless). The 31P chemical shift of 3 (δ 31P 150.6 ppm in CDCl3) is very close to that of 2. During the final aromatization step, notable quantities of the trans diastereomer of the 1,2-dhydrophosphinine 7 were recovered together with small quantities of the cis isomer 8. The R-proton is coupled to 31 P in 8 (δ5.10, 2JHP ) 9.4 Hz) and noncoupled in 7 (δ 4.83 2 JHP ) 0 Hz). These results are in line with the known dependency of the 2JHP coupling constants on the H-C-P-lone pair dihedral angle in cyclic phosphines.6 Their stereochemistry was definitively established by X-ray crystal structure analysis.
The structure of 8 is shown as an example (Figure 1). The H-C-P-Ph dihedral angle is 174.55°, and the Th-C-P-Ph angle is 72.43°. When 7 was heated at 250 °C over nickel powder, it was slowly transformed into phosphinine 3. On this (6) Albrand, J. P.; Gagnaire, D.; Robert, J. B. J. Chem. Soc., Chem. Commun. 1968, 1469.
10.1021/om8003256 CCC: $40.75 2008 American Chemical Society Publication on Web 06/26/2008
4006 Organometallics, Vol. 27, No. 15, 2008
Notes
nonannellated λ3-phosphinines. Thus, we decided to study the reactivity of 1-3 toward 2,3-dimethylbutadiene. Phosphaphenanthrene 1 reacts to give a complex mixture of products including the expected cycloadduct in low yield. On the contrary, dithienophosphinine (2) reacts cleanly but slowly with the diene at 140 °C, and 2-thienyldithienophosphine (3) gives a fast and quantitative reaction under the same conditions (eq 3).
Figure 1. Stereochemistry of 1,2-dihydrodithiophosphinine (8) as determined by X-ray crystal structure analysis.
basis, we propose the intermediacy of the λ5-phosphinine 9 in the aromatization reaction (eq 2).
The structure of 11 is depicted in Figure 2. It shows some disorder due to the presence of two orientations of the 2-thienyl substituent. The two annellating thieno rings are almost coplanar (interplane angle ca. 16°). The phosphorus atom is highly pyramidal: ∑C-P-C angles ) 295.7°. Apart from demonstrating the significant influence of thieno annellation and thienyl substitution on the chemistry of phosphinines, the synthesis of the highly annellated phosphines 10 and 11 could be of interest in homogeneous catalysis. Very bulky and highly annellated phosphines indeed seem to be very efficient as ligands in palladium-catalyzed reactions.8
Experimental Section The [1,2] suprafacial shift of the R-H from C to P can take place only in the cis isomer 8, and 7 must first undergo a pyramidal inversion at P before being converted into the phosphinine 3. Since 3 is yellow whereas 1 and 2 are colorless, we recorded the UV-vis spectrum of 3. The four bands of the spectrum of 2 at 236.1, 268.1, 286.0, and 347.9 nm are shifted in most cases toward longer wavelengths at 234.0, 271.0, 306.1, and 360.0 nm, confirming the significant influence of the substituent on the electronic structure of the phosphinine. In the same vein, DFT computations7 at the B3LYP/6-311+G(d,p) level indicated that the HOMO-LUMO gap is reduced by 0.16 eV when replacing Ph in 2 by Th in 3. This reduction mainly results from the lowering of the LUMO. A closer inspection of the computed structural data and Mulliken charges indicates that a significant charge transfer takes place from the thienyl substituent to the PdC double bond (Scheme 1). In our previous paper, we noticed that the HOMO and LUMO of 2 are highly localized at the PdC double bond and are shaped like the π and π* orbitals of a phosphaalkene. This observation suggested that 2 could react as a dienophile, contrary to (7) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, ReVision B.05; Gaussian, Inc.: Pittsburgh, PA, 2003.
Nuclear magnetic resonance spectra were obtained on a Bruker Avance 300 and Varian Inova spectrometer operating at 300.13 MHz for 1H, 75.45 MHz for 13C, and 121.496 MHz for 31P. Chemical shifts are expressed in parts per million downfield from external TMS (1H and 13C) and external 85% H3PO4 (31P). Mass spectra were obtained on VG 7070 and Hewlett-Packard 5989A GC/MS spectrometers. Elemental analyses were performed by Desert Analytics Laboratory, Tucson, AZ. 2-Hydroxy-1-phenyl-2-thienyl-1,2-dihydrodithienophosphinine Oxide (5). To a solution of dithienophosphole (4)4 (2.3 g, 8.4 mmol) in Et2O (50 mL) was added 4.5 mL of NEt3, then dropwise 5 mL of ThCOCl in Et2O (20 mL). The mixture was stirred for 1 h at room temperature and cooled at 0 °C, and 35 mL of degassed, distilled H2O was added. After stirring for 3 h at RT, the white precipitate was washed with H2O (3 × 30 mL) and Et2O (3 × 30 mL) and dried under vacuum (3.2 g, 95% yield). 31P NMR (THF): δ 20.6 ppm. MS: m/z 401 (MH+, 100%). Anal. Calcd for C19H13O2PS3: C, 56.98; H, 3.27. Found: C, 57.06; H, 3.69. 1-Phenyl-2-thienyl-1,2-dihydrodithienophosphinine Sulfide (6). A solution of 5 (3.2 g, 8 mmol) with Lawesson reagent (3 g, 7.5 mmol) in toluene (150 mL) was heated under reflux overnight at 120 °C. The cooled solution was hydrolyzed with a saturated solution of Na2CO3 (75 mL), and the toluene phase was washed with H2O (3 × 80 mL), dried on Na2SO4, and evaporated under vacuum. The residue was then chromatographed on silica gel with hexane/CH2Cl2 (2:3) as eluent. Compound 6 was isolated as a mixture of isomers, as light salmon crystals (2 g, 62% yield). 31 P NMR (CDCl3): δ 32.2. 1H NMR (CDCl3): δ 5.06 (d, 2JHP ) 14.1 Hz, CHTh). 13C NMR (CDCl3): δ 46.62 (d, 1JCP ) 50.1 Hz, CHTh). MS: m/z 401 (MH+, 100%). Anal. Calcd for C19H13PS4: C, 56.97; H, 3.27. Found: C, 57.00; H, 3.27. 2-Thienyldithienophosphinine (3) and Dihydro Derivatives 7 and 8. A solution of 6 (1.2 g, 3 mmol) and Ni (1.5 g) in toluene (5 mL) was heated in a pressure tube at 250 °C for 4 days. The (8) See, for example:Iwasawa, T.; Komano, T.; Tajima, A.; Tokunaga, M.; Obora, Y.; Fujihara, T.; Tsuji, Y. Organometallics 2006, 25, 4665.
Notes
Organometallics, Vol. 27, No. 15, 2008 4007 Scheme 1
solution was diluted with CH2Cl2, filtered, and evaporated. The residue was chromatographed on silica gel with hexane/CH2Cl2 (9: 1) as eluent. (a) Phosphinine 3 (first eluted product) was isolated as yellow crystals (0.26 g, 30% yield). 31P NMR (CDCl3): δ 150.6. 13C NMR (CDCl3): δ 137.53 (d, 3JC-P ) 10.3 Hz, Cγ phosphinine), 138.87 (d, 2JC-P ) 10.4 Hz, P-CdC), 141.35 (d, 2JC-P ) 13.8 Hz, PdCCS thieno), 144.06 (d, 2JC-P ) 32.2 Hz, PdC-CS thienyl), 155.08 (d, 1JC-P ) 59.9 Hz, P-CR thienyl), 156.56 (d, 1JC-P ) 48.3 Hz, P-CR thieno). The assignments have been made on the basis of a simulation by DFT (B3LYP/6-311+G(d,p)). MS: m/z 291 (MH+, 100%). Anal. Calcd for C13H7PS3: C, 53.77; H, 2.43. Found: C, 53.52; H, 2.31. (b) Phosphine 8 (second eluted product) was isolated as light yellow crystals (0.08 g, 6% yield). 31P NMR (CDCl3): δ -41.7. 1 H NMR (CDCl3): δ5.10 (s, 2JHP ) 9.4 Hz, H cis to lone pair, CHTh). 13C NMR (CDCl3): δ 39.80 (d, 1JCP ) 18.4 Hz, CHTh). Anal. Calcd for C19H13PS3: C, 61.93; H, 3.56. Found: C, 62.34; H, 3.89. (c) Phosphine 7 (third eluted product) was isolated as light orange crystals (0.40 g, 30% yield). 31P NMR (CDCl3): δ -30.6. 1H NMR (CDCl3): δ 4.83 (s, 2JHP ) 0 Hz, H trans to lone pair, CHTh). 13C NMR (CDCl3): δ 39.04 (d, 1JCP ) 16.9 Hz, CHTh). MS: m/z 385 (MH+ + O, oxidized species, 100%). Anal. Calcd for C19H13PS3: C, 61.93; H, 3.56. Found: C, 62.03; H, 3.80. X-ray monocrystals were obtained from CH2Cl2/hexane. [4+2] Cycloadducts 10 and 11. A solution of 2 (0.015 g, 0.05 mmol) and 2,3-dimethylbutadiene in excess (0.5 mL) in toluene (2 mL) was heated in a pressure tube at 140 °C and monitored by 31P NMR; the cycloaddition was complete after 50 h heating at 140
Figure 2. X-ray crystal structure of [4+2] cycloadduct 11. Main bond lengths (Å) and angles (deg): P1-C1 1.8079(14), P1-C9 1.8790(14), P1-C13 1.8504(14), C1-C4 1.3833(18), C4-C5 1.4602(19), C5-C8 1.3816(19), C8-C9 1.5126(19), C9-C10 1.5405(19), C10-C11 1.5154(19), C11-C12 1.338(2), C12-C13 1.512(2);C1-P1-C998.06(6),C1-P1-C13100.50(6),C9-P1-C13 97.13(6), C3-C4-C5-C6 15.99.
°C. The solution was then evaporated and chromatographed on silica gel with hexane/CH2Cl2 (4:1) as eluent. The cycloadduct 10 was isolated as white crystals (10 mg, 52% yield). 31 P NMR (CDCl3): δ -58.8. 13C NMR (CDCl3): δ 20.45 (s, Me), 22.10 (s, Me), 30.73 (d, 2JCP ) 13.8 Hz, CH2), 47.18 (d, 1JCP ) 12.27 Hz, CH2). MS: m/z 367 (MH+, 100%), 383 (MH+ + O, oxidized species, 90%). A solution of 3 (0.03 g, 0.1 mmol) and 2,3-dimethylbutadiene in excess (1 mL) in toluene (3 mL) was heated in a pressure tube at 140 °C for 5 h, then evaporated and chromatographed on silica gel with hexane/CH2Cl2 (4:1) as eluent. The cycloadduct 11 was isolated as white crystals (40 mg, quantitative yield). 31 P NMR (CDCl3): δ -55.5. 13C NMR (CDCl3): δ 20.47 (s, Me), 21.95 (d, 3JCP ) 6.14 Hz, Me), 31.48 (d, 2JCP ) 13.80 Hz, CH2), 47.64 (d, 1JCP ) 12.27 Hz, CH2). MS: m/z 373 (MH+, 100%); 389 (MH+ + O, oxidized species, 35%). Anal. Calcd for C19H17PS3: C, 61.26; H, 4.60. Found: C, 61.61; H, 4.99. X-ray monocrystals were obtained from CH2Cl2/Et2O/hexane. X-ray Structure Determination of 8 and 11. Measurements were carried out using a low-temperature device at T ) 100(2) K, on a Bruker X8-APEX9 KAPPA-CCD X-ray diffractometer system (Mo radiation, λ ) 0.71073 Å). The automated strategy determination program COSMO10 was used to define diffraction experiments on the basis of phi and omega scans. Frames were integrated using the Bruker SAINT version 7.06A software11 and using a narrow-frame integration algorithm. 8: a total of 13 999 reflections collected at a maximum 2θ angle of 58.66° (4320 independent reflections, Rint ) 0.0171, Rsig ) 0.0182, completeness ) 92.8%) and 3890 (90.05%) reflections were found greater than 2σ(I). Compound crystallized in the monoclinic cell, space group P2(1)/n, a ) 8.5061(7) Å, b ) 13.0337(11) Å, c ) 15.2990(13) Å, R ) 90.0°, β ) 90.0370(10)°, γ ) 90.0°, V ) 1696.1(2) Å3, Z ) 4, calculated density Dc ) 1.443 Mg/m3. 11: a total of 15 730 reflections collected at a maximum 2θ angle of 67.40° (6921 independent reflections, Rint ) 0.0296, Rsig 0.0442, completeness ) 99.0%) and 5345 (77.23%) reflections were found greater than 2σ(I). Compound crystallized in the monoclinic cell, space group P2(1)/c, a ) 8.0053(3) Å, b ) 8.6885(4) Å, c ) 14.3922(9) Å, R ) 103.068(4)°, β ) 92.171(3)°, γ ) 114.772(2)°, V )875.37(8) Å3, Z ) 4, calculated density Dc ) 1.413 Mg/m3. Absorption corrections were applied for all data using the SADABS program included in the SAINTPLUS software package.11 Direct methods using the Sir92 program12 were used for resolution. Direct methods of phase determination followed by a subsequent difference Fourier map led to an electron density map from which most of the non-hydrogen atoms were identified in the asymmetry unit. With subsequent isotropic refinement and some Fourier difference synthesis, all non-hydrogen atoms were identified, and atomic coordinates and isotropic and anisotropic displacement parameters of all the non-hydrogen atoms were refined by means of a full matrix least-squares procedure on F2, using SHELXTL (9) Bruker. APEX 2 version 2.0-2; Bruker AXS Inc.: Madison, WI, 2004. (10) COSMO NT Version 1.40; Bruker AXS Inc.: Madison, WI, XXXX. (11) SAINTPLUS Software Reference Manual, Version 6.02A; Bruker Analytical X-Ray System, Inc.: Madison, WI, 1997-1998. (12) SIR92, A program for crystal structure solution: Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl. Crystallogr. 1993, 26, 343.
4008 Organometallics, Vol. 27, No. 15, 2008 software.13 Hydrogen atoms were included in the refinement in calculated positions with isotropic thermal parameters fixed at 20% and 50% higher than Csp2 and Csp3 atoms, respectively, to which they were connected. Torsion angles were refined for methyl groups. The H(1) atom was isotropically refined for compound 8. For both compounds a statistical disorder generated by a free rotation was found for the thiophene ring. These were refined using restraints put on distances and bond angles in order to get a chemically correct model. The refinement converged at R1 ) 0.0331, wR2 ) 0.0829, with intensity I > 2σ(I), largest peak/hole in the final difference map 0.666 and -0.548 e Å-3 for 7 and R1 ) 0.0427, wR2 ) 0.1042, with intensity I > 2σ(I), largest peak/hole in the final difference map 0.698 and -0.302 e.Å-3 for 11. Drawings of molecules were achieved using ORTEP32.14 Further details on the (13) SHELXTL Software Reference Manual, Version 6.10; Bruker Analytical X-Ray System, Inc.: Madison, WI, 2000.
Notes crystal structure investigation are available on request from the Director of the Cambridge Crystallographic Data Centre, 12 Union Road, GB-Cambridge CB21EZ UK, on quoting the full journal citation.
Acknowledgment. The authors thank the CNRS and the University of California Riverside for the financial support of this work. Thanks are also due to Dr. Dan Borchardt for the UV/vis spectra. Supporting Information Available: X-ray crystal structure analyses of compounds 8 and 11. This material is available free of charge via the Internet at http://pubs.acs.org. OM8003256 (14) ORTEP3 for Windows: Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
